Chelating Effect of Siderophore Desferrioxamine-B on Uranyl Biomineralization Mediated by Shewanella putrefaciens

In contaminated water and soil, little is known about the role and mechanism of the biometabolic molecule siderophore desferrioxamine-B (DFO) in the biogeochemical cycle of uranium due to complicated coordination and reaction networks. Here, a joint experimental and quantum chemical investigation is carried out to probe the biomineralization of uranyl (UO₂²⁺, referred to as U(VI) hereafter) induced by Shewanella putrefaciens (abbreviated as S. putrefaciens) in the presence of DFO and Fe³⁺ ion. The results show that the production of mineralized solids {hydrogen-uranium mica [H₂(UO₂)₂(PO₄)₂·8H₂O]} via S. putrefaciens binding with UO₂²⁺ is inhibited by DFO, which can both chelate preferentially UO₂²⁺ to form a U(VI)-DFO complex in solution and seize it from U(VI)-biominerals upon solvation. However, with Fe³⁺ ion introduced, the strong specificity of DFO binding with Fe³⁺ causes re-emergence of biomineralization of UO₂²⁺ {bassetite [Fe(UO₂)₂(PO₄)₂·8(H₂O)]} by S. putrefaciens, owing to competitive complexation between Fe³⁺ and UO₂²⁺ for DFO. As DFO possesses three hydroxamic functional groups, it forms hexadentate coordination with Fe³⁺ and UO₂²⁺ ions via these functional groups. The stability of the Fe³⁺-DFO complex is much higher than that of U(VI)-DFO, resulting in some DFO-released UO₂²⁺ to be remobilized by S. putrefaciens. Our finding not only adds to the understanding of the fate of toxic U(VI)-containing substances in the environment and biogeochemical cycles in the future but also suggests the promising potential of utilizing functionalized DFO ligands for uranium processing.